The present invention relates to a method for manufacturing aspherical surfaces, particularly quadric surfaces such as elliptic, parabolic and hyperbolic surfaces.
Nowadays, spherical lenses and spherical reflecting mirrors have been widely used for optical systems, because they are easily available. However, if aspherical surfaces such as elliptic, hyperbolic and parabolic surfaces could be manufactured in a simple and accurate manner, they may be advantageously used in various optical systems. For instance, aspherical lenses and aspherical reflecting mirrors have been often used in order to eliminate or decrease aberrations. However, in practice, it is extremely difficult to manufacture the aspherical surfaces. It is a well known fact that it took several years to grind an aspherical reflecting mirror of a large diameter for use in an astronomical observatory. In this manner, at present, it is technically as well as economically difficult to utilize the aspherical optical systems to the full extent and thus, in the optical systems such as camera lens systems, various aberrations have to be corrected by combining a plurality of spherical lenses. This results in that the lens systems are liable to be complicated in construction, heavy in weight and large in size.
Heretofore, known methods for manufacturing the aspherical surfaces may be roughly classified into the following three methods.
(a) copy-grinding on the basis of a master curve
(b) press-molding of synthetic resin or glass material
(c) cutting under numerical control with using NC machine tools.
In the methods (a) and (b) use is made of a master which has to be manufactured by skilled workers almost in a manual manner. Moreover an accuracy of the master can not be made sufficiently high. Further in the method (c) using the NC machine tools, since a digital control is applied, a cut surface is inherently subjected to steps or stripes. This is particularly noticeable with a surface of large radius of curvature. In order to reduce such a drawback there has been developed an R interpolation method, but this solution could not assure the accuracy sufficiently. As described above, accurate aspherical surfaces could not be manufactured by the known methods and there has not been proposed any method for easily manufacturing aspherical surfaces having the required high accuracy.